SACRAMENTO, California  Environmental groups sued the U.S. Forest Service this week, claiming a six-year-old federal law aimed at preventing wildfires has degenerated into a backdoor effort to eventually increase logging across 340,000 acres of Sierra Nevada national forests.

The federal lawsuit challenges the Forest Service's effort to log 6,400 acres over five years in the Plumas National Forest west of Quincy, California, where a coalition of loggers and local conservationists once met to propose what eventually became national fire-prevention policy.

The Forest Service says the clearing project will reduce the risk of catastrophic wildfire near the small Sierra mountain town of Meadow Valley, while providing local logging jobs.

The logging in the Plumas forest is the first to be approved under the federal law, but the government has proposed logging a total of 340,000 acres in nearby parts of other national forests.

The environmental groups say the plan allows the cutting of bigger, more fire-resistant trees in an area already cleared of smaller, more flammable material. They say it also would destroy 4,280 acres of old trees around 16 California spotted owl nesting sites.

Forest Service spokesman Matt Mathes said the 6,400 acres are unique, because the agreement "specifically requires us to promote the economic health of that area, and part of that is helping the local timber industry."

Chad Hanson of the John Muir Project, which was among the groups that sued, said the government's response is a ruse.

"There's nothing in the law that requires them to log the largest 1 percent of the trees remaining in that area," he said, adding that jobs could just as well be provided by cutting smaller trees and brush or providing other services.

The suit seeks to force the Forest Service to conduct a full environmental impact review before it permits logging of large trees.